Hello, Thanks for posting your query. It is true that endometriosis can form deposits anywhere, though extraperitoneal formations are rare. Investigation is needed to establish the cause. It is possible that a peritoneal deposit is causing referred pain to the rib as the nerve innervation is common. Further management can be planned accordingly. Hormone courses to inhibit ovulation are likely to help along with anti-prostaglandin medication. Hope your query has been clarified. Take care.